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<body class="bg-gray-50">
    <!-- Hero Section -->
    <section class="hero text-white py-20 px-4 sm:px-6 lg:px-8">
        <div class="max-w-4xl mx-auto text-center">
            <div class="inline-block px-4 py-1 mb-4 text-sm font-semibold text-indigo-100 bg-white bg-opacity-20 rounded-full">
                <i class="fas fa-code mr-2"></i>Java集合框架
            </div>
            <h1 class="text-4xl md:text-5xl font-bold mb-6 leading-tight">深入理解HashSet的独特机制</h1>
            <p class="text-xl md:text-2xl opacity-90 max-w-3xl mx-auto">
                HashSet如何确保元素唯一性？底层基于HashMap的实现机制剖析与最佳实践
            </p>
            <div class="mt-10 flex justify-center">
                <div class="w-24 h-1 bg-white bg-opacity-30 rounded-full"></div>
            </div>
        </div>
    </section>

    <!-- Main Content -->
    <div class="max-w-4xl mx-auto px-4 sm:px-6 lg:px-8 py-12">
        <!-- Introduction -->
        <div class="mb-16">
            <div class="flex items-center mb-6">
                <div class="feature-icon mr-4">
                    <i class="fas fa-unlock-alt"></i>
                </div>
                <h2 class="text-3xl font-bold text-gray-800">核心概念</h2>
            </div>
            <p class="text-lg text-gray-700 mb-6">
                <code class="font-mono bg-gray-100 px-2 py-1 rounded">HashSet</code>是Java集合框架中的重要成员，它提供了一种不允许重复元素的高效集合实现。了解其底层机制对于编写高效、健壮的Java代码至关重要。
            </p>
            <div class="highlight mb-8">
                <p class="text-lg font-medium mb-2"><i class="fas fa-lightbulb text-yellow-500 mr-2"></i>关键特性</p>
                <ul class="list-disc pl-5 space-y-2">
                    <li>基于<code class="font-mono bg-gray-100 px-1 py-0.5 rounded">HashMap</code>实现，元素作为key存储</li>
                    <li>不允许重复元素，通过<code class="font-mono bg-gray-100 px-1 py-0.5 rounded">equals()</code>和<code class="font-mono bg-gray-100 px-1 py-0.5 rounded">hashCode()</code>确保唯一性</li>
                    <li>添加、删除、查找操作的平均时间复杂度为O(1)</li>
                    <li>不保证元素的顺序，特别是它不保证顺序会随时间保持不变</li>
                </ul>
            </div>
        </div>

        <!-- Section 1 -->
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                <h2 class="text-3xl font-bold text-gray-800">1. 唯一性保证</h2>
            </div>
            <div class="bg-white rounded-xl shadow-md overflow-hidden card">
                <div class="p-6">
                    <p class="text-gray-700 mb-4">
                        <code class="font-mono bg-gray-100 px-2 py-1 rounded">HashSet</code>的核心特性之一是它不允许重复的元素。它通过使用<code class="font-mono bg-gray-100 px-1 py-0.5 rounded">HashMap</code>来实现这一点。在<code class="font-mono bg-gray-100 px-1 py-0.5 rounded">HashSet</code>中，元素的唯一性是通过<code class="font-mono bg-gray-100 px-1 py-0.5 rounded">equals</code>方法来检查的。如果尝试添加一个已经存在的元素，<code class="font-mono bg-gray-100 px-1 py-0.5 rounded">HashSet</code>会忽略这个添加操作。
                    </p>
                    
                    <!-- Visualization -->
                    <div class="mt-8 mb-6">
                        <div class="mermaid">
                            graph LR
                            A[add(element)] --> B{元素是否已存在?}
                            B -->|是| C[忽略操作]
                            B -->|否| D[添加到集合中]
                        </div>
                    </div>
                </div>
            </div>
        </div>

        <!-- Section 2 -->
        <div class="mb-16">
            <div class="flex items-center mb-6">
                <div class="feature-icon mr-4">
                    <i class="fas fa-layer-group"></i>
                </div>
                <h2 class="text-3xl font-bold text-gray-800">2. 实现机制</h2>
            </div>
            <div class="bg-white rounded-xl shadow-md overflow-hidden card">
                <div class="p-6">
                    <p class="text-gray-700 mb-4">
                        <code class="font-mono bg-gray-100 px-2 py-1 rounded">HashSet</code>使用<code class="font-mono bg-gray-100 px-1 py-0.5 rounded">HashMap</code>来存储元素。每个元素都作为<code class="font-mono bg-gray-100 px-1 py-0.5 rounded">HashMap</code>的键存储，值通常是一个固定的常量（例如，<code class="font-mono bg-gray-100 px-1 py-0.5 rounded">Boolean.TRUE</code>）。<code class="font-mono bg-gray-100 px-1 py-0.5 rounded">HashMap</code>本身不允许有重复的键，因此<code class="font-mono bg-gray-100 px-1 py-0.5 rounded">HashSet</code>也不能有重复的元素。
                    </p>
                    
                    <div class="mt-6 mb-4">
                        <div class="flex items-center text-sm font-medium text-indigo-600 mb-2">
                            <i class="fas fa-project-diagram mr-2"></i>
                            HashSet与HashMap关系图
                        </div>
                        <div class="mermaid">
                            classDiagram
                                class HashSet {
                                    -map: HashMap
                                    +add(E e) boolean
                                    +remove(Object o) boolean
                                    +contains(Object o) boolean
                                }
                                class HashMap {
                                    -table: Node[]
                                    +put(K key, V value) V
                                    +get(Object key) V
                                    +remove(Object key) V
                                }
                                HashSet --> HashMap : 使用
                        </div>
                    </div>
                </div>
            </div>
        </div>

        <!-- Section 3 -->
        <div class="mb-16">
            <div class="flex items-center mb-6">
                <div class="feature-icon mr-4">
                    <i class="fas fa-redo"></i>
                </div>
                <h2 class="text-3xl font-bold text-gray-800">3. 如何处理重复元素</h2>
            </div>
            <div class="bg-white rounded-xl shadow-md overflow-hidden card">
                <div class="p-6">
                    <p class="text-gray-700 mb-4">
                        当你向<code class="font-mono bg-gray-100 px-2 py-1 rounded">HashSet</code>添加一个元素时，<code class="font-mono bg-gray-100 px-1 py-0.5 rounded">HashSet</code>会首先计算元素的哈希码，然后检查是否已经存在具有相同哈希码的元素。如果存在，它会使用<code class="font-mono bg-gray-100 px-1 py-0.5 rounded">equals</code>方法来进一步检查元素的等价性。如果两个元素相等，添加操作会被忽略。
                    </p>
                    
                    <div class="mt-6 mb-4">
                        <div class="code-block rounded-lg overflow-hidden">
                            <pre class="p-4 text-sm"><code class="language-java">import java.util.HashSet;
import java.util.Set;

public class HashSetDemo {
    public static void main(String[] args) {
        Set&lt;String&gt; set = new HashSet&lt;&gt;();
        set.add("Alice");
        set.add("Bob");
        set.add("Alice"); // 尝试添加重复元素

        System.out.println("HashSet 中的元素：");
        for (String element : set) {
            System.out.println(element);
        }
    }
}</code></pre>
                        </div>
                        <div class="mt-4 text-sm text-gray-600">
                            <i class="fas fa-info-circle text-indigo-500 mr-2"></i>在上面的代码中，<code class="font-mono bg-gray-100 px-1 py-0.5 rounded">HashSet</code>只会存储一次<code class="font-mono bg-gray-100 px-1 py-0.5 rounded">"Alice"</code>，即使你尝试添加它多次。输出结果会是：
                        </div>
                        <div class="code-block rounded-lg overflow-hidden mt-2">
                            <pre class="p-4 text-sm"><code class="language-plaintext">HashSet 中的元素：
Alice
Bob</code></pre>
                        </div>
                    </div>
                </div>
            </div>
        </div>

        <!-- Section 4 -->
        <div class="mb-16">
            <div class="flex items-center mb-6">
                <div class="feature-icon mr-4">
                    <i class="fas fa-exclamation-triangle"></i>
                </div>
                <h2 class="text-3xl font-bold text-gray-800">4. 注意事项</h2>
            </div>
            <div class="grid md:grid-cols-2 gap-6">
                <div class="bg-white rounded-xl shadow-md overflow-hidden card">
                    <div class="p-6">
                        <h3 class="text-xl font-semibold text-gray-800 mb-3">
                            <i class="fas fa-tachometer-alt text-indigo-500 mr-2"></i>性能考虑
                        </h3>
                        <p class="text-gray-700">
                            <code class="font-mono bg-gray-100 px-1 py-0.5 rounded">HashSet</code>在处理添加、删除和查找操作时具有很好的性能。平均情况下，插入、删除和查找操作的时间复杂度是O(1)。然而，性能依赖于良好的哈希函数实现。
                        </p>
                    </div>
                </div>
                <div class="bg-white rounded-xl shadow-md overflow-hidden card">
                    <div class="p-6">
                        <h3 class="text-xl font-semibold text-gray-800 mb-3">
                            <i class="fas fa-cube text-indigo-500 mr-2"></i>自定义对象
                        </h3>
                        <p class="text-gray-700">
                            如果使用自定义对象作为<code class="font-mono bg-gray-100 px-1 py-0.5 rounded">HashSet</code>的元素，确保正确重写<code class="font-mono bg-gray-100 px-1 py-0.5 rounded">equals</code>和<code class="font-mono bg-gray-100 px-1 py-0.5 rounded">hashCode</code>方法，以确保对象的唯一性判断能够正确工作。
                        </p>
                    </div>
                </div>
            </div>
        </div>

        <!-- Section 5 -->
        <div class="mb-16">
            <div class="flex items-center mb-6">
                <div class="feature-icon mr-4">
                    <i class="fas fa-user-edit"></i>
                </div>
                <h2 class="text-3xl font-bold text-gray-800">5. 自定义对象的例子</h2>
            </div>
            <div class="bg-white rounded-xl shadow-md overflow-hidden card">
                <div class="p-6">
                    <p class="text-gray-700 mb-4">
                        下面的示例展示了如何为自定义类正确实现<code class="font-mono bg-gray-100 px-1 py-0.5 rounded">equals</code>和<code class="font-mono bg-gray-100 px-1 py-0.5 rounded">hashCode</code>方法，以确保它们在<code class="font-mono bg-gray-100 px-1 py-0.5 rounded">HashSet</code>中正常工作。
                    </p>
                    
                    <div class="mt-6">
                        <div class="code-block rounded-lg overflow-hidden">
                            <pre class="p-4 text-sm"><code class="language-java">import java.util.HashSet;
import java.util.Objects;
import java.util.Set;

class Person {
    private String name;
    private int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null || getClass() != obj.getClass()) {
            return false;
        }
        Person other = (Person) obj;
        return age == other.age && Objects.equals(name, other.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, age);
    }

    @Override
    public String toString() {
        return "Person{name='" + name + "', age=" + age + "}";
    }
}

public class HashSetCustomObjectDemo {
    public static void main(String[] args) {
        Set&lt;Person&gt; set = new HashSet&lt;&gt;();
        set.add(new Person("Alice", 30));
        set.add(new Person("Bob", 25));
        set.add(new Person("Alice", 30)); // 尝试添加相同的对象

        System.out.println("HashSet 中的元素：");
        for (Person person : set) {
            System.out.println(person);
        }
    }
}</code></pre>
                        </div>
                    </div>
                </div>
            </div>
        </div>

        <!-- Summary -->
        <div class="bg-indigo-50 rounded-xl p-8 mb-16">
            <h2 class="text-2xl font-bold text-indigo-800 mb-4">
                <i class="fas fa-check-circle text-indigo-600 mr-2"></i>关键要点总结
            </h2>
            <ul class="space-y-3 text-indigo-900">
                <li class="flex items-start">
                    <i class="fas fa-check text-indigo-500 mt-1 mr-2"></i>
                    <span><code class="font-mono bg-indigo-100 px-1 py-0.5 rounded">HashSet</code>通过<code class="font-mono bg-indigo-100 px-1 py-0.5 rounded">HashMap</code>实现，利用键的唯一性保证元素唯一</span>
                </li>
                <li class="flex items-start">
                    <i class="fas fa-check text-indigo-500 mt-1 mr-2"></i>
                    <span>添加元素时先比较<code class="font-mono bg-indigo-100 px-1 py-0.5 rounded">hashCode</code>，再通过<code class="font-mono bg-indigo-100 px-1 py-0.5 rounded">equals</code>确认是否重复</span>
                </li>
                <li class="flex items-start">
                    <i class="fas fa-check text-indigo-500 mt-1 mr-2"></i>
                    <span>自定义对象必须正确实现<code class="font-mono bg-indigo-100 px-1 py-0.5 rounded">equals</code>和<code class="font-mono bg-indigo-100 px-1 py-0.5 rounded">hashCode</code>方法</span>
                </li>
                <li class="flex items-start">
                    <i class="fas fa-check text-indigo-500 mt-1 mr-2"></i>
                    <span>基本操作时间复杂度为O(1)，性能优异</span>
                </li>
                <li class="flex items-start">
                    <i class="fas fa-check text-indigo-500 mt-1 mr-2"></i>
                    <span>不保证元素的顺序，适用于不需要维护插入顺序的场景</span>
                </li>
            </ul>
        </div>
    </div>

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